brown necrotic areas along the stalk itself. Although P. destructor does not usually kill the entire onion plant, the pathogen reduces the growth of the onion.Bulb: The bulb tissue typically becomes soft and watery, lacking the firm quality that typical healthy onions have. The outer portion of the bulb also appears wrinkled and may take on an amber hue. Environment Environmental conditions are key to the growth and spread of Peronospora destructor. Spores are generally dispersed during periods of high or low humidity regardless of the temperature at the time. The optimal temperature for P. destructor spore germination is 10 °C, and less sporulation occurs as the temperature increases. Oospores may be produced at up to 27 °C, however, most spores grow when temperatures are cooler. During the summer, oospores induce hyphal growth into the leaf tissue of the onions, in which sporangiophores emerge. The sporangiophores then release sporangia, which are most often spread by wind, in which the pathogen may be capable of traveling several miles before reaching a new host plant. After growing on a host for approximately 9–16 days, the sporangia can sporulate and are available for dispersal to new hosts as part of a secondary disease cycle. As the season ends, Peronospora destructor overwinters in leaf debris as mycelium, and in the soil as oospores. The disease of downy mildew as a whole is most likely to grow on plants that are in cool and damp environments, however, the pathogen has different ways of utilizing environmental factors depending on the condition. For example, if the host plant is in a rainless region, morning dew may create conditions that are suitable for downy mildew to grow. Rainless regions in which Peronospora destructor is found include Saudi Arabia, Iraq, Lebanon, Libya, and Turkey. ControlChemical Control: One method of control for P. destructor is the use of chemical pesticides. Fungicides such as dithiocarbamates, chlorothalonil, copper, ametoctradin/dimethomorph, and fenamidone may be applied to plants when early symptoms are present. Fungicides should be applied on a more regular basis when the weather is cool and damp (seven-day intervals) compared to when weather is cool and dry (ten-day intervals). By using chemical methods early in the disease cycle, P. destructor is less likely to continue reproducing throughout the plant.Cultural Control: Another method of control is at the field level which includes rotating Allium species with other plants that are not hosts of